1. Field of the Invention
The present invention relates to an exposure information setting device for a camera for applying the aperture value of the lens to the exposure operation circuit as digital information by means of the aperture value setting mechanism.
2. Description of the Prior Art
In the case of an automatic exposure control camera (AE camera) provided with the an electrical control circuit, in order to set the aperture value of the lens (in the case of the shutter time priority photography) generally, the value of the element in the electrical circuit is varied by displacing the aperture value setting member in the camera body in functional engagement with the aperture value ring. For example, the resistance value is varied by making the contact piece provided on the set member move slidingly over the resistance body in such a manner that the aperture value is converted into an analog signal with the voltage or the current value thus obtained so as to be applied to the exposure operational circuit of the camera. In the case of such an analog information setting, the high precision cannot be achieved due to the variation of the temperature characteristics and of the resistance characteristics of the resistance body, the wear of the resistance body due to the sliding, the noise formation due to the variation of the pressure of the contact and so on, whereby the cost increase can not be avoided due to the application of special materials.
In order to improve the above mentioned shortcomings of the conventional device, various systems has been proposed for directly obtaining a digital information from the displacement of the aperture value setting member in order not to use the analog information. Even in the case of the setting device of such a digital system, the device becomes unavoidably complicated in order to directly obtain a digital information such as of binary code, grey code and so on from the displacement of the setting member. Thus, for example, in order to digitalize the whole range of the aperture values which are divided into 32 steps, an encoder of 5 bits becomes necessary and, in order to treat this encoder, five contact pieces becomes necessary. That is, a number of contact pieces are arranged electrically independent from each other or five resistance bodies are arranged independent from each other so that it is very difficult to build the arrangement in a limited space such as in a camera body.
On the other hand, there is a method for producing a single "on" signal or a single "off" signal by making the contact pieces move slidingly over a comb tooth shaped conductor pattern instead of directly producing a digital information such as in binary code, grey code and so on from the displacement of the setting member. By means of such an encoder, the composition of the pattern becomes remarkable simple, whereby the on or the off signal as mentioned above can be obtained by making a contact piece move slidingly over the comb tooth shaped conductor pattern in such a manner that the pattern can be constituted compact and fine so that it is very profitable also from the view point of space. However, in the case of the system for setting the aperture value by means of the combination of such comb tooth shaped pattern with a contact piece the scanning directive of the contact piece, is limited to only one. Therefore, in case of the scanning method in accordance with which the contact piece is displaced to and fro optionally, the member of the then produced pulses often does not correspond to the aperture value. Namely, the number of the pulses produced when a contact piece scans the comb tooth shaped conductor pattern is in proportion to the number of the contacts not made between the contact piece and the conductor pattern in such a manner that the number of the input pulses corresponds to the aperture value in the case of the one direction scanning with the contact piece while the number of the input pulses continues to increase in the case of the to and fro scanning with the contact piece out of the proportion to the aperture value. Thus such a system as mentioned above has not been applied to the camera.
A purpose of the present invention is to eliminate the above mentioned shortcoming by enabling the signal obtained from the to and fro scanning of a pair of comb tooth shaped conductor patterns having a phase difference, with a contact piece to be applied to the exposure amount control circuit through the phase sorting circuit.
Further purposes of the invention will be disclosed from the explanations to be made later in accordance with the embodiments in the accompanying drawings.